economic impact of maritime trade and the shipping industry of canals and rivers?

Answer 1

Are you looking to today or to the past?

If the latter, look at the great cities of the world and note how many of them are on the water. There is a reason for that.

Ditto for the great expense in constructing canals - not just the famous ones such as at Suez and Panama, but older like the Erie Canal in New York State, etc. The first seems to have been built about 6000 years ago:
http://en.wikipedia.org/wiki/Canal
http://home.eznet.net/~dminor/Canals.html
http://my.ohio.voyager.net/~lstevens/canal/

If today, look at just how much traffic passes through U.S. ports such as Long Beach,
http://www.polb.com/about/port_stats/5_yr_comparisons.asp

Oakland,
http://www.portofoakland.com/maritime/facts_operations.asp

New York, etc.
http://www.panynj.gov/DoingBusinessWith/seaport/html/trade_statistics.html

Then consider that Singapore, Hong Kong, and Amsterdam/Rotterdam are bigger yet. Ditto for barge traffic on the Mississippi, Missouri, and Illinois Rivers.

The U.S. Maritime Admin has the statistics for the U.S. (Check out the pdf file entitled "U.S. Water Transportation Statistical Snapshot" at this site:
http://www.marad.dot.gov/MARAD_statistics/